1. Field of the Invention
The present invention relates to an optical scanning apparatus which makes a light beam scan on a surface-to-be-scanned in a main scanning direction and an image forming apparatus which forms an electrostatic image using such an optical scanning apparatus.
2. Description of the Related Art
An apparatus which uses this type of optical scanning apparatus is an image forming apparatus such as a laser printer, a copier machine and a facsimile machine. For instance, in the apparatus described in Japanese Patent Application Laid-Open Gazette No. 63-279220, a laser beam modulated in accordance with image data impinges upon a deflector via a collimator lens, a first cylindrical lens and a reflection mirror and is hence deflected. More specifically, the specific structure of the apparatus described in the Japanese Patent Application Laid-Open Gazette No. 63-279220 is as follows.
In this optical scanning apparatus, a laser beam emitted from a semiconductor laser passes through a collimator lens and a cylindrical lens, and the laser beam is accordingly shaped into such a laser beam whose cross sectional shape is a sideways-elongated elliptic shape which elongates in the main scanning direction. This laser beam impinges upon a reflecting mirror of a deflector along a main scanning surface.
To solve various problems which accompany use of a polygon mirror or a galvanometer mirror as a deflector, this apparatus uses a deflector which is manufactured utilizing a micro machining technique. In short, utilizing a photolithographic technique, an etching technique, etc., a substrate of crystal, glass, silicon or the like is processed into an optical deflection element in which a drive coil, a reflecting mirror and a ligament are formed integral with a frame. The deflector comprising this optical deflection element deflects a laser beam which is incident upon the reflecting mirror, as a voltage is applied upon the drive coil and the reflecting mirror can consequently pivot about a pivot axis which is approximately orthogonal to the main scanning direction.
The laser beam deflected by the deflector is imaged on an image forming member (which corresponds to the “latent image carrier” of the present invention) via a scanning lens and a second cylindrical lens. An electrostatic latent image which corresponds to image data is formed on the image forming member in this manner.